Question

    A boat travels 30 km downstream in 2 hours and the same

    distance upstream in 5 hours. Find the speed of the boat in still water and the speed of the stream.
    A Boat speed = 15 km/h, stream speed = 45 km/h Correct Answer Incorrect Answer
    B Boat speed = 17.5 km/h, stream speed = 1.5 km/h Correct Answer Incorrect Answer
    C Boat speed = 10.5 km/h, stream speed = 4.5 km/h Correct Answer Incorrect Answer
    D Boat speed = 17.5 km/h, stream speed = 3.5 km/h Correct Answer Incorrect Answer

    Solution

    Downstream speed = 30/2 = 15 km/h Upstream speed = 30/5 = 6 km/h Let boat speed in still water = u, stream speed = v. u + v = 15 u − v = 6 Add: 2u = 21 ⇒ u = 10.5 km/h Then v = 15 − 10.5 = 4.5 km/h Answer: Boat speed = 10.5 km/h, stream speed = 4.5 km/h.

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